Polymers for use as filtration control aids in drilling muds

ABSTRACT

The instant invention is directed to a polymer, having an intrinsic viscosity of 1.0 to 7.0, preferably 1.5 to 5.0, dl/g in 1.0 M NaCl, prepared from: 
     (A) 2.5 to 45%, by weight, of at least one unsaturated carboxylic acid, or its salt; 
     (B) 5.0 to 85%, by weight, of at least one unsaturated sulfonic acid, or its salt; 
     (C) 2.5 to 15%, by weight, of at least one unsaturated cationic-containing monomer; and 
     (D) 0 to 90%, by weight, of at least one unsaturated non-ionic monomer. 
     The instant invention is also directed to the polymer in combination with an aqueous clay dispersion and the use of the admixture as a filtration aid in drilling muds.

This is a division of application Ser. No. 674,215, filed Nov. 23, 1984,now U.S. Pat. No. 4,652,623.

BACKGROUND OF THE INVENTION

It is well known that in perforating earthen formations to tapsubterranean deposits such as gas or oil, that perforation isaccomplished by well drilling tools and a drilling fluid. The drillingfluid serves to cool and lubricate the drill bits, to carry the cuttingsto the surface as the drilling fluid is circulated in and out of thewell, to support at least part of the weight of the drill pipe and drillbit, to provide a hydrostatic pressure head to prevent caving of thewalls of the well bore, to deposit on the surface of the well bore afilter cake which acts as a thin, semi-impervious layer to prevent unduepassage therethrough of fluids, and to perform other functions as arewell known in the drilling art. It is important that the drilling fluidexhibit a relatively low rate of filtration or fluid loss in addition tohaving desirable rheological properties such as viscosity and gelstrength. It is also important that the drilling fluid system should bekept as simple and inexpensive as possible in order to avoid undueexpense in the drilling of the well.

Drilling fluid also has an effect on the friction between the drill pipeand the bore hole, and the higher the coefficient of friction betweenthe drill pipe and the formation being drilled, that is, the lower thedegree of lubricity of the drilling fluid, the greater the powerrequirements needed to rotate the drill pipe in the bore hole filledwith the drilling fluid. Further in this respect, a drilling fluidhaving a low degree of lubricity or a high coefficient of frictionbetween the drill pipe and the uncased well bore means that a highdegree of drag on the drill pipe results, thereby lessening the usefullife of the drill pipe. Therefore, the lubricating properties of thedrilling fluid are assuming an increased importance to those skilled inthe art, not only with regard to the wearing of the bearings in thedrill bit, but also with respect to the friction between the drill pipeand the uncased bore hole.

Drilling an oil or gas well is generally conducted by a rotary system.This system depends upon the rotation of a string of drill pipe to thebottom of which is attached a multi-pronged drilling bit. The bit cutsinto the earth causing the cuttings to accumulate as drilling continues.As a result, a drilling fluid must be used to carry these cuttings tothe surface for removal, thus allowing the bit to continue functioningand the bottom hole to be kept clean and free of cuttings at all times.Drilling systems other than the rotary system are sometimes used, butthese also require a drilling fluid to remove the bore hole cuttings andto perform functions related to drilling fluids.

Oil-producing formations are generally porous layers having varyingdegrees of permeability to the flow of fluids such as oil, water or gas.Consequently, the rate of oil production is largely determined by therate of flow through these permeable formations which, in turn, isdependent upon the porosity or permeability of the sand or stonepresent. In drilling through such a porous layer, it is desirable toemploy a drilling fluid having such characteristics that excessiveamounts of liquids or solids are prevented from penetrating through theporous formation. The ability of the drilling fluid to prevent excessiveformation fluid penetration is called filtration control.

Besides the filtration control, an acceptable polymer has to maintain anadequate rheology (flow) properties of drilling fluids. Gary and Darley,ed., Composition and Properties of Oil Well Drilling Fluids, 4th ed.,page 12, states: "The flow properties of the drilling fluid play a vitalrole in the success of the drilling operation. These properties areprimarily responsible for removal of the drill cuttings, but influencedrilling progress in many other ways. Unsatisfactory performance canlead to such serious problems as bridging the hole, filling the bottomof the hole with drill cuttings, reduced penetration rate, holeenlargement, stuck pipe, loss of circulation, and even a blowout".

Materials that have been used in the past to control filtration rates ofaqueous drilling fluids by plugging, producing cakes or similar methods,have included materials such as pregelatinized starch, sodiumcarboxylmethylcellulose (CMC), sodium polyacrylates and lignites. Eachof these materials have certain limitations. For example, lignitebecomes ineffective in high salt concentrations. Thermodegradation ofCMC is accelerated as the temperature approaches 300° F.

Acrylic and methacrylic derivatives, such as those which arecopolymerized with hydrocarbon substituted styrenes, such as alphamethyl styrene, para methyl styrene, 2,4-dimethyl styrene and the likehave been utilized in drilling fluids. For example, U.S. Pat. No.2,718,497 teaches the use of relatively high molecular weight polymersof these materials control water loss characteristics of aqueous mudsand clay dispersions. Additionally, U.S. Pat. No. 2,650,905 teaches theuse of water soluble sulfonated polystyrene derivatives for filtrationcontrol in water-based drilling fluids.

Acrylic acid derivatives such as copolymers of acrylamide and sodiumacrylate derivatives have been frequently used commercially asflocculants for drilling fluids, and are disclosed in U.S. Pat. Nos.3,558,545 and 3,472,325. Similarly, a copolymer derived from acrylicacid and acrylamide is disclosed in U.S. Pat. No. 3,323,603 as aflocculant for aqueous drilling fluids. However, the use of polyacrylatefor filtration control in some areas has been limited by its sensitivityto calcium ions.

U.S. Pat. No. 4,293,427 discloses a copolymer additive prepared from (1)a (meth)acrylamido alkyl sulfonic acid or alkali metal salt thereof and(2) a (meth)acrylamide or N-alkyl (meth)-acrylamide. The copolymer maybe cross-linked with a quaternary ammonium salt.

DESCRIPTION OF THE INVENTION

The instant invention is directed to a polymer, having an intrinsicviscosity of 1.0 to 7.0, preferably 1.5 to 5.0, dl/g in 1.0 M NaCl,prepared from:

(A) 2.5 to 45%, preferably 25 to 35%, by weight, of at least oneunsaturated carboxylic acid, or its salt;

(B) 5.0 to 85%, preferably 25 to 40%, by weight, of at least oneunsaturated sulfonic acid, or its salt;

(C) 2.5 to 15%, preferably 5 to 10%, by weight, of at least oneunsaturated cationic-containing monomer; and

(D) 0 to 90%, preferably 15 to 45% by weight, of one or more unsaturatednonionic monomer.

The instant invention is also directed to an aqueous drilling fluid,comprising:

(a) an aqueous clay dispersion; and

(b) the above-described polymer.

The instant invention is also directed to a method for drilling a wellin a subterranean formation comprising circulating into the well, duringdrilling an aqueous drilling fluid, the improvement wherein said aqueousdrilling fluid comprises:

(a) an aqueous clay dispersion; and

(b) the above-described polymer.

The clay dispersion may be any finely divided solid which is capable ofbeing dispersed or suspended in an aqueous liquid vehicle. Ordinarily,such material will include hydratable clay or colloidal clay bodies suchas Wyoming bentonite, commercial medium-yield drilling clays mined invarious parts of the country such as in Texas, Tennessee and Louisiana,and those produced when clay subsurface formations are drilled.Weighting materials added to increase specific gravity such as barites,iron oxide, and the like may also be included.

The aqueous medium may be fresh water such as is obtained from wells orstreams; it may be salt water from the sea or from wells; or, it mayeven include oil-in-water emulsions, i.e., water which has becomecontaminated in some way with small quantities of oil, or to which suchoil has been added to gain some desired advantage. The polymers of theinstant invention were found to be particularly effective in salt waterand to be stable at high temperature. The drilling mud containing thepolymers of the instant invention showed both good filtration andrheology properties.

It is contemplated that the drilling muds of the invention may alsocontain other additives besides the polymers of the invention. Materialssuch as caustic, quebracho, lime and the like may be added to thedrilling mud at the surface while other materials such as gypsum, shaleand the like may be encountered in subsurface formations during drillingoperations.

When employed in accordance with the invention, the polymer may be addeddirectly to the drilling mud as a dry powder, as a slurry suspended in asuitable liquid, or as a solution in water or some other suitablesolvent, and they may be incorporated therein at any convenient point inthe mud circulation system. It may be desirable to employ a mixingdevice such as a cone and jet mixer or the equivalent for incorporatingthe additive in the mud.

Any unsaturated carboxylic acid or its salt, may be used in preparingthe polymer. Examples include acrylic acid, methacrylic acid, vinylacetic acid, allyl acetic acid, 4-methyl-4-pentenoic acid, α-haloacrylicacid, maleic acid, itaconic acid, fumaric acid, β-hydroxyethylacrylate,β-carboxyethyl acrylate, their salts and mixtures thereof. The preferredcarboxylic functional monomers are acrylic acid, methacrylic acid,β-carboxyethylacrylate and their salts.

Any unsaturated sulfonic acid, or its salt, may be used. Examplesinclude 2-acrylamido-2-methyl propyl sulfonic acid (AMPS),2-methacrylamido-2-methyl propyl sulfonic acid (MAMPS), styrene sulfonicacid (SSA), vinyl sulfonic acid (VSA), sulfoalkylacrylates ormethacrylates, allyl sulfonic acid (ASA), methallyl sulfonic acid(MASA), 3-methacrylamido-2-hydroxypropyl sulfonic acid, their salts andmixtures thereof. The preferred sulfonic compounds are AMPS, MAMPS, ASA,MASA, SSA, VSA and their salts.

Any unsaturated cationic-containing compound may be used. Specificexamples of the most preferred cationic-containing monomers includequaternary ammonium compounds, such as diethyldiallyl ammonium chloride(DEDAAC) dimethyldiallyl ammonium chloride (DMDAAC), methacryloyloxyethyl trimethyl ammonium methylsulfate (METAMS), methacrylamido propyltrimethyl ammonium chloride (MAPTAC), acryloyloxyethyl trimethylammonium chloride (AETAC), methacryloyloxyethyl trimethyl ammoniumchloride (METAC), acrylamidoethylpropyl trimethyl ammonium chloride(AMPTAC), acrylamido methyl butyl trimethyl ammonium chloride (AMBTAC)and mixtures thereof. The preferred cationic-containing monomers areDMDAAC, DEDAAC and METAC.

The polymer may also be prepared by polymerizing a monomer containing atertiary amine as the pendant group with subsequent quaternization ofthe nitrogen in the polymer to form the cationic mer units. Likewise,sulfur and phosphorus-containing monomers may be exhaustively methylatedto form cations.

Any non-ionic monomer may optionally be used. Examples include:acrylamide, and its derivatives, such as methacrylamide, andN,N-dimethyl acrylamide. The preferred non-ionic monomer is acrylamide.Mixtures of non-ionic monomers may be used in preparing the polymer.

The quantity of the polymer to be employed in the drilling mud of theinvention will vary with circumstances over a reasonably wide range andthe amount employed in a specific suspension or dispersion will dependon these circumstances and the characteristics of the drilling fluidtreated. Any quantity which reduces the water loss may be used.Ordinarily, satisfactory results with regard to water loss reductionwill be obtained with quantities ranging between one and four pounds per42-gallon barrel of drilling mud. For optimum reduction in filtrationrate with certain drilling muds, however, quantities up to 6 pounds per42-gallon barrel may be required. On the other hand, in some caseswhere, for example, only small improvement in filtration rate isdesired, as little as 0.125 pound of the additive per barrel of mud willproduce the desired effect. The exact amount to be added, as previouslypointed out, depends upon the original character of the mud and on theproperties desired. This can be determined, as is customary in the fieldby simple tests at the time the addition is made.

The polymers may be prepared by mixing the monomers preferably in thepresence of a free radical initiator. Any free radical initiator may beused. Examples include peroxides, azo initiators and redox systems. Thepolymerization may also be initiated photochemically. The preferredcatalysts are a mixture of persulfate, bisulfite and any azo typeinitiator, such as 2,2'-azobis-(2-amidinopropane)hydrochloride.

The polymer may be made by any of a variety of procedures, for example,in solution, suspension, bulk and emulsions.

The temperature is not critical. The reaction will generally occurbetween 10° and 100° C. The reaction, depending on the temperature,generally takes from 1 to 12 hours. Measuring for residual monomer willverify when the reaction is complete.

The pH of the reaction mixture is not critical. The pH is generally inthe range of 4.5 to 9.0.

The percent solids in the reaction mixture is not critical. Thepreferred range is 1 to 50%, by weight, solids.

The molecular weight of polymers are difficult to accurately measure.The polymers are, instead, usually identified by intrinsic viscosity.The intrinsic viscosity of the polyampholyte is not critical in theinstant invention. The preferred intrinsic viscosity to 1.0 to 7.0 dl/g,most preferably 1.5 to 5.0 dl/g.

The rheology properties were measured by a direct-reading Fann V-Gmeter.

The following measurements are generally used for evaluation:

(a) Plastic viscosity (PV)=Reading at 600 rpm

Reading at 300 rpm (cps)

Plastic viscosity is the part of flow resistance caused by mechanicalfriction.

(b) Yield Point (YP)=Reading at 300 rpm - PV (lb/100 sq. ft.). YieldPoint, the second component of resistance to flow in a drilling fluid,is a measurement of the electro-chemical or attractive forces in a mud.

(c) Gel strength (GELS)=Reading at 3 rpm initially/

Reading at 3 rpm after 10 minutes

GELS is a measure of the attractive forces between mud solids understatic conditions. Lower gel values indicate lower pump pressurerequired to break circulation.

(d) The filtration property was measured by a standard API fluid loss(FL) test (FL=30-minute fluid loss from filter press at 100 psi of N₂).

The above testing procedures are outlined in the American PetroleumInstitute Bulletin, "The Rheology of Oil Well Driiling Fluids", #13D,Section 5.3 and "Standard Procedure for Field Testing Drilling Fluids",#13B, Section 2.5.

Mud Compositions A. Sea Salt Mud

15 g of bentonite in 250 ml of distilled water, 17.5 g of a simulatedsea salt (Sea Rite) in 100 ml of distilled water, 20 g of Rev-dust, 2.0g of polymer were sequentially added with mixing. The plastic viscosity(PV), yield point (YP), gel strength (GELS) and fluid loss (FL) weremeasured. The results are summarized in Table II.

B. 5% KCl Mud

Bentonite was prehydrated by adding 10 g of bentonite to 250 ml ofdistilled water and mixed for 10 minutes. 18 g of KCl dissolved in 100ml of distilled water, and 2.0 g of polymer were sequentially added withmixing. The PV, YP, GELs and FL were measured. The results aresummarized in Table II.

C. Calcium sulfate (gyp) Mud

14 g of bentonite in 350 ml distilled water, 20 g of Rev-dust, 4 g ofgypsum and 1.0 of polymer were sequentially added with mixing. The PV,YP, GELs and FL were measured. The results are summarized in Table II.

EXAMPLE 1-11

The polymers of the Examples were produced by mixing the monomersindicated in Table I, in the amounts, initiator, temperatures (initialand peak) and times indicated. For comparison examples:

Example A: A 67/33 weight ratio AM/AMPS copolymer, prepared according toU.S. Pat. No. 4,293,427, Example 1. No acrylate and cationic units inthe polymer.

Example B: A 67/33 weight ratio AM/AMPS copolymer with 1.48 weightpercent METAMS crosslinker, prepared according to U.S. Pat. No.4,293,427, Example 1. No acrylate unit in the polymer.

Example C: A 47/43/10 weight ratio AA/AM/DMDAAC terpolymer. No AMPS inthe polymer.

Example D: A commercial carboxylmethyl cellulose type polymer (DrispacSuperlo).

                                      TABLE I                                     __________________________________________________________________________    REACTION CONDITIONS                                                           Polymers %, by Weight*       INITIATOR         t.sub.i                                                                          t.sub.p                                                                          T.sub.Total              Example                                                                            AA.sup.a                                                                         AMPS.sup.b                                                                         AM.sup.c                                                                         DMDAAC.sup.d                                                                         METAC.sup.e                                                                         Type                                                                              Amount                                                                             Type                                                                              Amount                                                                             (°C.)                                                                     (°C.)                                                                     (Minutes)                __________________________________________________________________________    1    60 30   -- 5      5     SPS.sup.f                                                                         .16% SMBS.sup.g                                                                        .04% 22 87 47                       2    30 30   35 5.0    --    SPS .32% SMBS.sup.g                                                                        .16% 14 80 27                       3    35 25   35 5.0    --    SPS .32% SMBS                                                                              .16% 25 98  8                       4    25 25   45 5.0    --    SPS .32% SMBS                                                                              .16% 24 98  8                       5    25 35   35 5.0    --    SPS .32% SMBS                                                                              .16% 23 87 12                       6    35 35   25 5.0    --    SPS .32% SMBS                                                                              .16% 24 87 11                       7    30 30   30 10.0   --    SPS .16% SMBS                                                                              .04% 19 83 15                       8    30 30   30 5.0    5.0   SPS .16% SMBS                                                                              .04% 22 84 31                       9    30 30   30 5.0    5.0   SPS .16% SMBS                                                                              .04% 21 83 38                                                    V-50.sup.h                                                                        .004%                                        10   30 30   30 5.0    5.0   SPS .16% SMBS                                                                              .04% 21 85 40                                                    V-50                                                                              .004%                                        11   30 30   30 5.0    5.0   SPS .16% SMBS                                                                              .04% 19 77 35                                                    V-50                                                                              .004%                                        __________________________________________________________________________     *Polymer concentration = 28%                                                  .sup.a AA = acrylic acid                                                      .sup.b AMPS = 2acrylamido-2-methyl propyl sulfonic acid (AMPS is a            registered trademark of The Lubrizol Corporation.)                            .sup.c AM = acrylamide                                                        .sup.d DMDAAC = dimethyldialkyl ammonium chloride                             .sup.e METAC = methacryloyloxymethyl trimethyl ammonium chloride              .sup.f SPS = sodium persulfate                                                .sup.g SMBS = sodium metabisulfite                                            .sup.h V50 = 2,2azobis-(2-amidinopropane)hydrochloride                   

                                      TABLE II                                    __________________________________________________________________________    PERFORMANCE DATA.                                                                     Polymer  KC1          SEA SALT     GYP MUD                            EXAMPLE [η] in 1.0 M NaCl                                                                  PV YP GELS                                                                              FL PV YP GELS                                                                              FL PV YP GELS                                                                              FL                       __________________________________________________________________________    1       2.6      5  1  1/1 10 5  9  4/7 13 4  13 10/10                                                                             39                       2       2.0      4  1  1/1 12 5  2  1/1 10 6  1  1/1 12                       3       2.2      5  0  1/1 10 6  0  1/1 7  4  1  1/1 10                       4       2.2      5  2  1/1 9  6  1  1/2 7  5  1  1/1  9                       5       2.1      5  1  1/1 11 6  0  1/1 7  4  1  1/1 11                       6       1.9      5  0  1/1 14 7  1  1/1 9  5  0  1/1 14                       7       4.1      5  4  1/1 8  8  3  2/2 8  6  8  7/7 29                       8       3.8      7  2  1/1 9  9  1  1/1 6  5  11 10/10                                                                             21                       9       4.3      8  2  1/1 9  9  2  1/1 7  6  9  7/8 16                       10      --       8  4  1/1 9  9  2  2/3 6.5                                                                              6  7  3/7 16                       11      --       8  3  1/1 9  8  3  1/2 5.5                                                                              5  6  2/3 14                       Comparative A    -- -- --  -- -- -- --  -- 10 25 15/15                                                                             10                       Comparative B    -- -- --  -- -- -- --  -- 8  23 14/14                                                                             12                       Comparative C    -- -- --  -- -- -- --  -- 5  11 11/11                                                                             65                       __________________________________________________________________________

EXAMPLE 12

This Example demonstrates the effectiveness of the polymer of thepresent invention as a filtration control agent at high temperature. Thepolymer of Example 9, was added to a modified gypsum mud with thefollowing composition:

    ______________________________________                                        D1 H.sub.2 O    350          ml                                               Bentonite       14           g                                                Rev-Dust        30           g                                                Gypsum          4            g                                                Caustic         0.75         g                                                Lignosulfate    3.0          g                                                Polymer Sample  1.0          g                                                ______________________________________                                    

Each sample was aged for 16 hours at a temperature of 325° F. and thencooled down. The rheological properties and API filtrate reading weretaken. A commercial carboxylmethyl cellulose sample, as identified ascomparative D, was also examined. The results of these tests are shownin Table III.

                  TABLE III                                                       ______________________________________                                        Sample    Hot Aged     PV     YP    GELS  FL                                  ______________________________________                                        Example 9 No           7      3     0/2    9.8                                Example 9 325° F., 16 hrs.                                                                    4      1     0/1   19.8                                Comparative D                                                                           No           8      2     0/4    9.4                                Comparative D                                                                           325° F., 16 hrs.                                                                    4      5     0.5/9 47.6                                Base Mud  No           3      10     7/12 57.4                                Base Mud  325° F., 16 hrs.                                                                    6      9      4/14 56.6                                ______________________________________                                    

What is claimed is:
 1. An aqueous drilling fluid comprising:(i) anaqueous clay dispersion; and (ii) a polymer, having an intrinsicviscosity of 1.0 to 7.0 dl/g in 1.0 M NaCl, prepared from:(A) 25 to 35%,by weight, of at least one unsaturated carboxylic acid selected from thegroup consisting of acrylic acid, methacrylic acid and their salts; (B)25 to 40%, by weight, of at least one unsaturated sulfonic acid selectedfrom the group consisting of 2-acrylamido-2-methylpropyl sulfonic acid,2-methacrylamido-2-methylpropyl sulfonic acid, and their salts; (C) 5 to10%, by weight, of at least one unsaturated cationic containing monomerselected from the group consisting of dimethyldiallyl ammonium chloride,dimethyldiallyl ammonium chloride and methacryloyloxyethyl trimethylammonium chloride; and (D) 15 to 45%, by weight, of at least oneunsaturated non-ionic monomer selected from the group consisting ofacrylamide and methacrylamide.
 2. The aqueous drilling fluid of claim 1,wherein said polymer has an intrinsic viscosity of 1.5 to 5.0 dl/g in1.0 M NaCl.
 3. A method for drilling a well in a subterranean formation,comprising circulating into the well, during drilling, an aqueousdrilling fluid, the improvement wherein said aqueous drilling fluidcomprises:(i) an aqueous clay dispersion; and (ii) a polymer, having anintrinsic viscosity of 1.0 to 7.0 dl/g in 1.0 M NaCl, prepared from:(A)25 to 35%, by weight, of at least one unsaturated carboxylic acidselected from the group consisting of acrylic acid, methacrylic acid andtheir salts; (B) 25 to 40%, by weight, of at least one unsaturatedsulfonic acid selected from the group consisting of2-acrylamido-2-methylpropyl sulfonic acid,2-methacrylamido-2-methylpropyl sulfonic acid, and their salts; (C) 5 to10%, by weight, of at least one unsaturated cationic containing monomerselected from the group consisting of dimethyldiallyl ammonium chloride,dimethyldiallyl ammonium chloride and methacryloyloxyethyl trimethylammonium chloride; and (D) 15 to 45%, by weight, of at least oneunsaturated non-ionic monomer selected from the group consisting ofacrylamide and methacrylamide.